how can I use a brush CUSTOM re-topology?
Strenght Brush = 0 with Constant Detail

I usually take advantage of the Constant Detail dynotopology mode for this task. Basically the detail size does not depend anymore on the brush size on the screen, but it's a function of the Resolution parameter field.



Given that we can set up a brush that deoes nothing (set the Strenght to 0) but modify the topology with the set resolution. With the eyedropper we can easily pick up the resolution of the nearby faces like shown in the image sequence below.



You can restrict the action of the brush to Subdivide only or Collpase only if wanted. There's even the "Detail Flood Fill" button to automatically spread the same amount of resolution across the whole model.